Polyurethane elastomer moldings having a surface skin have been prepared by a reaction mixture in a closed mold reaction injection molding (RIM) process by reacting polyether polymer triols and/or diols with aromatic chain extenders, such as diethyl toluene diamine and aromatic isocyanates, such as MDI (see for example U.S. Pat. No. 4,218,543, incorporated by reference). In this patent polyurethane elastomer moldings have been prepared employing aromatic diamines as chain extenders with aromatic isocyanates like 4, 4'-diiosocyanatodiphenylmethane polyisocyanates with a polyol having a molecular weight of from about 1800 to 12,000. Reaction injecting molding (RIM) requires large machines because of the fast reaction and gel times involved, while the presence of urea linkages in the resulting elastomeric product provides for higher heat distortion temperatures and green strengths. Most RIM parts employing the patent process require post curing and elaborate painting techniques, while the painted parts can easily scratch and chip requiring touchup work.
Solventless compositions for preparing sprayable polyurethanes and poly(urea)urethanes have been disclosed employing an isocyanate terminated prepolymer or a quasi-prepolymer prepared from aromatic isocyanates, such as TDI and MDI, as well as hexamethylene diisocyanate. The isocyanate prepolymer is reacted with a curing agent of a highly reactive polyol or polyamine or combinations thereof, including for example, a methylenedianiline curing agent. The reaction components are intimately admixed and sprayed through an atomizing nozzle onto a surface to produce the desired polyurethane or poly(urea)urethane coating which is essentially a solventless sprayable coating (see for example U.S. Pat. No. 4,267,299, incorporated by reference).
Polyurethane coatings have also been prepared by reacting an isocyanate prepolymer, such as a prepolymer based on 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane with a polyalkylene ether polyol together with a aromatic diamine, such as the aromatic diamines described in U.S. Pat. No. 4,218,543. The reaction mixture produces an elastomeric polyurethane coating which is essentially solvent-free or a low solvent coating composition.